Seals are generally arranged to provide sealing between two or more parts of a structure. One or more of the parts may be movable relative to the other parts and a seal arranged to provide a degree of sealing between the parts for at least part of that movement. Aircraft comprise aerofoils, which generally comprise fixed aerofoil structures and a set of one or more control surfaces that are moveable relative to the fixed aerofoil. The control surfaces are arranged to be moveable so as to modify the aerodynamic qualities of the aerofoil and thus enable control of the aircraft in flight. For at least some control surfaces, their function is improved if a seal is maintained between the control surface and the fixed aerofoil for at least a predetermined part of the movement relative to the aerofoil. Such seals enable continuity of airflow over the interface between the fixed aerofoil and the control surface. Seals may also prevent leakage of air between the aerofoil and the control surface, which may otherwise have a detrimental effect on the function of the aerofoil or the control surface.